The present invention relates to a touch-panel input device overlayed on a liquid crystal panel, CRT or the like. An operator presses the device in a position corresponding to displayed information. The device determines the position pressed and sends appropriate command input data to a processing device such as a personal computer. The source of pressure on the device can be from a pen, finger or the like. More specifically, the present invention relates to a touch-panel input device that achieves improved visibility by sealing a transparent insulative fluid between transparent plates.
In general, touch-panel input devices are found on the display screen of a liquid crystal panel, CRT, or the like where an operator can select information by touching an appropriate area of the display. The touch-panel input device reacts to pressure applied to a transparent surface to indicate a specific position according to the contents of the display. The touch-panel device detects the display position selected and generates corresponding command input data. The generated command input data is then sent to a processing device such as a personal computer.
Touch-panel input devices of this type generally contain a movable plate positioned over a substrate. The substrate and movable plate are constructed to maintain a gap between the movable plate and the substrate when they are overlayed. The substrate and movable plate have conductive layers on the surfaces that face each other across the insulative gap. The conductive layers are made from transparent materials to provide visual access to the display screen. However, the presence of air between the substrate and the movable plate creates a large refraction index differential. This large refraction index differential results in a transmittance efficiency of 80%, making the screen difficult to view.
The difficulty in viewing the display screen is addressed in touch-panel input devices such as in Japanese laid-open patent publication number 64-14630 and Japanese laid-open patent publication number 2-105916. These publications disclose a solution to the above difficulty by injecting a transparent, insulative fluid between the substrate and the movable plate. The fluid has a refraction index that is close to that of the materials used in the substrate and the movable plate, thus reducing reflectivity and improving transmittance.
Referring to FIG. 5 and FIG. 6, there is shown a conventional touch-panel input device 100. A thin transparent plate 101 is a movable plate and transparent substrate 102 is a thick substrate that faces a display device (not shown). A frame-shaped spacer 105 is layered between transparent plate 101 and transparent substrate 102 to form a slight gap.
Transparent conductor layers 103, 104 are composed of an Indium Tin Oxide (ITO) film or the like, printed on the facing surfaces of transparent plate 101 and transparent substrate 102. The ITO film is printed on the facing surfaces with a uniform thickness. Leads 103a, 103b, 104a and 104b are also printed on these facing surfaces to provide electrical connections for transparent conductor layers 103, 104. A voltage generated at a contact point between transparent conductor layers 103, 104 is measured on the electrical path provided by leads 103a, 103b, 104a and 104b. The measured voltage at the contact point enables detection of the position at which transparent plate 101 is pressed.
Transparent conductor layers 103, 104 are usually separated by spacer 105. Dot spacers 106 are printed on transparent conductor layer 104 at regular intervals sufficient to prevent light pressure applied to transparent plate 101 from causing accidental contact between the transparent conductor layers 103, 104. Dot spacers 106 are composed of an insulative composite resin such as epoxy resin. Dot spacers 106 augment the gap separation provided by spacer 105 to prevent position from being detected when transparent plate 101 is accidentally or lightly touched.
Spacer 105 is composed of a tacking agent 105b applied to upper and lower surfaces of a thin plate 105a. A sealed space between transparent conductor layers 103, 104 and within spacer 105 is formed by tacking thin plate 105a to transparent plate 101 and transparent substrate 102. Thin plate 105a is tacked to transparent plate 101 and transparent substrate 102 at the perimeters of transparent conductor layers 103, 104.
Transparent plate 101 can move horizontally (in the direction indicated by the arrow in FIG. 6) over tacking agent 105b while maintaining a sealed space between transparent conductor layers 103, 104. This configuration provides a close, tight contact between transparent plate 101 and spacer 105, while at the same time permitting transparent plate 101 to move elastically over thin plate 105a in a horizontal direction. When pressure is applied to transparent plate 101, the region surrounding the point of contact is uniformly flexed toward transparent substrate 102. The flexure of transparent plate 101 remains uniform, even if the point of contact is near spacer 105 in a perimeter region of transparent plate 101.
Once a sealed space between transparent conductor layers 103, 104 is achieved, a transparent insulative fluid 107 is injected into the space. Transparent insulative fluid 107 has a refraction index that is relatively close to the refraction indices for the transparent conductor layers 103, 104. For example, ITO has a refraction index of 1.9, while silicon oil, an example of a transparent insulative fluid 107, has a refraction index of 1.4.
Interposing transparent insulative fluid 107 between transparent conductor layers 103, 104 reduces the amount of light reflected by touch-panel input device 100 when exposed to an illumination source (not shown) located above touch-panel input device 100. Since transparent insulative fluid 107 has a refraction index relatively close to that of transparent conductor layers 103, 104, overall light transmittance increases to around 90%. The light reflected by touch-panel input device 100 is correspondingly reduced, thus significantly improving visibility of the display screen.
In this type of conventional touch-panel input device 100, pressure is applied to transparent plate 101 to create contact between transparent conductor layer 104 and opposing transparent conductor layer 103. The width of the gap between conductor layers 103, 104 is kept small to provide reliable contact and other advantages. One means of keeping the gap width small is to interpose between transparent conductor layers 103, 104 as a thin film. Transparent insulative fluid 107 then provides insulation between transparent conductor layers 103, 104 with a small gap width. However, the applied pressure to transparent plate 101 needed to create contact between transparent conductor layers 103, 104 increases significantly.
The increased pressure needed to create contact between transparent conductor layers 103, 104 can be achieved by use of a dedicated input device such as a stylus pen. The stylus pen applies increased pressure per unit area which makes reliable input more consistent. However, the addition of a stylus pen further complicates device operation by increasing the number of parts and slowing user input. Also, the stylus pen can be lost, which makes the device difficult to operate.
In addition to requiring greater pressure, the use of a person's finger to operate the device results in greater contact area. A curved surface such as a person's finger having a curvature radius of, for example, 25 mm, creates a relatively broad area of contact when applied to transparent plate 101. This broad area of contact requires increased pressure per unit area to assure contact between transparent conductor layers 103, 104. Such a large pressure requirement results in inadequate contact between transparent conductor layers 103, 104, unless a person presses very hard with a finger. Such a high pressure is difficult to achieve for all users, and also difficult to maintain.
Thus, when the device is used in operations such as tracing, drawing figures or characters, or dragging an icon or pointer, excessive pressure must be used to obtain reliable results. To achieve consistent results, a person must therefore apply a high pressure with a finger, which is difficult and tiring.